JEITA CP-3451
- 70 -
Stipulations on image height
Image height information consists of the valid image height tag (PixelYDimension), SOF marker information, and
JPEG compressed data. Of these three, the recording of a valid image height tag is mandatory.
The image height is padded in the following case. The padding value is not specified.
a) When the image height is not an exact multiple of 16 and the JPEG block has unused capacity to be filled.
Insertion of a restart marker does not require padding. The method of recording the various image height data with
and without padding is given in Figure 31. The SOF marker always has the same value as the effective image
height tag.
Figure 31 Image Data Height Description
Table 20 gives examples of information recorded in the direction of image height and padding data height, for each
of cases A, B, and C of Figure 31.
Table 20 Typical Height Direction Information and Padding Data (when Y:Cb:Cr = 4:2:2)
Valid Image Height
Valid Image Height
Tag
SOF Information
Compressed Data
Padding Height
A
480
480
480
480
0
B
474
474
474
480
6 (< 1MCU)
C
460
460
460
464
4 (< 1MCU)
B. Image size reproduction procedure in the Exif reader
It is recommended that the Exif reader (and in particular, dedicated software) follow the procedure shown in Figure
32 for reproducing images. First it expands the image based on the SOF information. Next it trims the image on the
right and lower edges in accord with information in the valid image width tag and height tag, and reproduces the
valid image data. If the SOF information and the valid image width and height tag information are the same,
trimming is unnecessary.
X=multiple of 16 ?
PixelYDimension = Y
SOF.Y = Y
Padding in
multiple of 64 ?
JPEG Compression
No
Yes
Y
: Valid Image length
SOF.Y
: Vertical line value in SOF
PixelYDimension : PixelYDimension value
A
B,C